In general, LED (Light-Emitting Diode) chips are used in light-emitting devices of surface-mounting types that are used as a light source for various display panels, a backlight for liquid crystal displays and a light source for lighting switches. Each LED chip consists of a p-side semiconductor and an n-side semiconductor that are joined into a p-n junction. FIG. 13 shows one example of light-emitting devices wherein such chip parts are used.
In this light-emitting device 60, LED chips 62, which have a n-side semiconductor layer 62a and a p-side semiconductor layer 62b that are mutually joined into a p-n junction, are used. The n-side semiconductor layer 62a of this LED chip 62 is affixed onto a lead frame 61.
The p-side semiconductor layer 62b, which forms the upper surface of the LED chip 62, is electrically connected to a frame 63 on the anode side, which is adjacent to the lead frame 61, by a bonding wire 64 made of a gold line or other lines with a diameter of approximately 10 .mu.m to 40 .mu.m. Here, the bonding wire 64 is shaped like an arc above, the LED chip 62 so as not to be cut off by the edges or other portions of the LED chip 62. Moreover, one part of the lead frame 61 and one part of the frame 63 on the anode side are sealed by light-transmitting resin 65 in a manner so as to cover the LED chip 62 and the bonding wire 64.
FIG. 14 is a side view showing one example of light-emitting devices wherein such chip parts are used. In this light-emitting device 70, LED chips 74 are used that have a n-side semiconductor layer 74a and a p-side semiconductor layer 74b that are mutually joined into a p-n junction. In this light-emitting device 70, electrode patterns 72 and 73 are formed by metal plating at respective ends in the length-wise direction of the surface of an insulating substrate 71. The electrode patterns 72 and 73 are bent down from the surface of the insulating substrate 71 along the respective end faces thereof in the length-wise direction, thereby covering the respective end portions of the bottom surface of the insulating substrate 71. Here, the n-side semiconductor layer 74a is affixed onto one of the electrode patterns 72.
The p-side semiconductor layer 74b, which forms the upper surface of the LED chip 74, is electrically connected to the other electrode pattern 73 of the insulating substrate 71 by a bonding wire 75 made of a gold line or other lines with a diameter of approximately 10 .mu.m to 40 .mu.m. Here, the bonding wire 75 is shaped like an arc above the LED chip 74 so as not to be cut off by the edges or other portions of the LED chip 74. Further, the LED chip 74 is sealed by light-transmitting resin 76 together with the bonding wire 75.
As described above, the bonding wires 64 and 75, which are highly susceptible to cutoffs due to external stress, are respectively sealed by the light-transmitting resins 65 and 76.
However, when, upon manufacturing the light-emitting device 60 or the light-emitting device 70, the bonding wire 64 or 75 is soldered to the frame 63 or the electrode pattern 73, the bonding wire 64 or 75 still tends to be cut off. Moreover, the bonding wire 64 or 75 also tends to be cut off by external stress caused by warps or other phenomena of the frame 63 and the insulating substrate 71 that occur after the soldering process.
Furthermore, it is necessary for the bonding wire 64 or 75 to have a distance of approximately 100 .mu.m to 200 .mu.m from the top of the arc formed on the LED chip 62 or 74 to the surface of the LED chip 62 or 74 so as not to be cut off by the edges or other portions of the LED chip 62 or 74. As a result, the light-transmitting resin 65 or 76 needs to be thick to the order of 100 .mu.m above the arc so as to also seal the arc that is formed by the bonding wire 64 or 75. This makes the light-transmitting resin 65 or 76 thicker, causing the light-emitting device 60 or 70 to become bulky.
Moreover, when an LED chip 74, mounted on the insulating substrate 71, is sealed by light-transmitting resin 76, some of the light-transmitting resin 76 in the molten state tends to adhere to the bottom surface of the insulating substrate 71. The light-transmitting resin 76, thus adhered to the bottom surface of the insulating substrate 71, causes adverse effects on wiring and other elements that are installed on the bottom surface of the insulating substrate 71. For this reason, it is necessary to prevent the light-transmitting resin 76 in its molten state from trickling down to the bottom surface of the insulating substrate 71.
In general, when the LED chip 74 is sealed by the light-transmitting resin 76, a jig, a metal mold or other members, which is used to prevent the light-transmitting resin 76 in its molten state from trickling along the side face of the insulating substrate 71 down to the bottom surface, is tightly pressed onto a portion along the edge of the insulating substrate 71. For this reason, it is necessary to provide an area for accepting the jig or other members along the edge of the insulating substrate 71. This also causes the light-emitting device 70 to become bulky.
Moreover, in order to mass-produce light-emitting devices, a number of through holes are formed in an insulating substrate, and a number of LED chips are disposed on the insulating substrate and are sealed by light-transmitting resin. Then, the insulating substrate and light-transmitting resin are subjected to dicing cuts so as to be shaped into each LED chip. In particular, in this arrangement, the light-transmitting resin in its molten state tends to trickle down to the bottom surface of the insulating substrate passing the through holes. For this reason, it is necessary to provide areas for accepting the jigs or other members around the respective through holes.
FIG. 15 shows one example of the minimum dimensions of the light-emitting device 70 of the chip type of FIG. 14. In this light-emitting device 70, a square LED chip 74, each side measuring 300 .mu.m, was used. In this case, the thickness of the insulating substrate 71 was at least 200 .mu.m, the thickness of the LED chip was 300 .mu.m, the distance from the top of the arc of the bonding wire 75 to the upper surface of the LED chip 74 was 200 .mu.m, and the thickness of the light-emitting resin 76 covering the arc was 100 .mu.m. Therefore, the minimum necessary thickness of the light-emitting device 70 was 800 .mu.m.
Furthermore, the length (area) of the insulating substrate 71 in the lengthwise direction, which is required to mount the LED chip 74, was 600 .mu.m, the length required for separating the electrode pattern 73 and the electrode pattern 72 from each other was 200 .mu.m, the length required for connecting the bonding wire 75 and the electrode pattern 73 was 400 .mu.m, and the length required for placing the jig or other members, which is used to prevent the light-transmitting resin 76 installed on the insulating substrate 71, from trickling down to the bottom surface of the insulating substrate 71, was 200 .mu.m along the entire edge of the insulating substrate 71. Therefore, the length of the insulating substrate 71 in the lengthwise direction, which forms the length of the light-emitting device 70 in the lengthwise direction, was 1600 .mu.m (1.6 mm), the minimum necessary length.
In recent years, in order to meet demands for compactness of various display panels, lighting switches and other apparatuses, compact light-emitting devices have been required. Therefore, it is not desirable to have thick light-transmitting resin 65 or 76. However, the thinner the light-transmitting resin 65 or 76 is made, the higher the possibility of cutoff of the bonding wire 64 or 75. This results in a problem of low reliability in light-emitting devices to be produced.